Separation of minerals having different specific gravities in a body of liquid medium



May 27, 1952 F. F. RIDLEY 2,598,305

SEPARATION OF MINERALS HAVING DIFFERENT SPECIFIC GRAVITIES IN A BODY OF LIQUID MEDIUM Filed July 26, 1949 2 SHEETS-SHEET 1 lwenlor Attorney;

May 27, 1952' F. F. RIDLEY SEPARATION OF MINERALS HAVING DIFFERENT SPECIFIC IES IN A BODY OF LIQUID MEDIUM GRAVIT Filed July 26, 1949 2 SHEETS-SHEET 2 Nut Inv nlor EMA ELJKZ tlorneyS Patented May 27, 1952 SEPARATION OF MINERALS HAVING DIF- FERENT SPECIFIC GRAVITIES IN A BODY OF LIQUID MEDIUM Frank Frost Ridley, Ponteland, England Application July 26, 1949, Serial No. 106,952 In Great Britain July 29, 1948 3 Claims. (Cl. 209-173) This invention relates to the separation of minerals having different specific gravities in a body of liquid medium of density intermediate those of the minerals being separated, wherein the heavier material sinks through the liquid and settles on a frictional conveying surface which continuously moves the sinks from the separating zone and raises them out of the liquid by frictional contact between the sinks and the conveying surface, when they are discharged, the lighter materials being separately collected at the surface and discharged. Examples of this method of and apparatus for separation are set forth in U. S. Patents Nos. 2,486,682 and 2,489,161.

This method of separation is advantageous in that the efficiency of the float and sink separation is enhanced by the influence of the frictional conveyance of the sinking material because only material which is actually denser than the liquid can be conveyed in this manner, and consequently there is no tendency of loss of lighter materials in the sinks product. For the most efficient conditions of frictional conveying, the liquid medium which is in contact with the surface should flow in the same direction as the surface and at similar speed; This is of advantage because it enables material of intermediate gravity which is onlyvery slightly denser than the liquid to have better frictional contact with the surface and thereby be more readily conveyed by it. If there were no flow, or the flow were in a contrary direction to the movement of the surface, the material only slightly denser than the liquid would meet with some fiuid resistance and thereby would not so readily grip the surface and be conveyed by it.

The object of this invention is to enhance the effect of frictional conveying by maintaining the flow of the liquid medium in the same direction as that of the movement of the surface throughout its full length and travel until the sinks are discharged from the liquid medium, thereby enabling material which is only very slightly denser than the liquid to maintain adhesion with the surface and be conveyed by it throughout its length of travel. Another objectis at the same time to provide improved means for regulating the amount, distribution and direction of flow of liquid medium in diiferent zones of the body of the separating medium. A still further object is to provide improved means for effecting the removal of the middlings. A still further object is to provide means whereby such middlings may be removed at will separately or with the floats.

In the particular apparatus described and shown in the above patent specifications the liquid was caused to flow in the direction of the belt until the floating materials were discharged at the surface. After this discharge the further flow with the belt was maintained by side weirs in the tank. These latter however, did not maintain a continuous flow to the extreme end and across the width of the belt owing totheir posi-v tions at the sides of the tank.

With the apparatus according to the invention the conveying surface of the belt is caused to discharge slightly below the liquid level atone extreme end of the body of liquid medium while a flow of liquid medium is induced immediately above the conveying surface in the same direction as and throughout the travel of the conveyed sinks, the said flow discharging with the sinks at the liquid level.

since the discharge point of the conveying surface is slightly below the liquid level the liquid fiows over the end of the conveying surface with the sinks, the flow thus being across the width and not at the sides, and flow is thus maintained to the extreme end of the body of liquid.

The apparatus according to a troughed invention has the belt passing over a delivery pulley located outside the tank at or slightly belowthe liquid level in said tank, the said belt discharge being adaptedto discharge liquid medium with the sinks in the direction of travel of the belt, and at the feed end of the tank, liquid inlet means adapted to feed liquid medium above the belt to induce flow in the direction of travel of the sinks throughout the length of the carrying portion of the said belt.

The belt troughing is maintained between the discharge end of the tank and the delivery pulley so that the-upturned edges of the belt retain the liquid within the width of the belt and prevent overflow at the'sides before the delivery point is reached. This troughing may be caused by mitred rollers set to lead the belt in a gentle curvefrom the tank to the pulley. The belt may be troughed throughout its length by making the tank floor of transversely concave section and the troughing is then maintained from the end of the tank to the delivery pulley as above described.

The floats are preferably discharged over a weir into a transverse trough which projects downwardly into the body of liquid medium. This trough may be suitably shaped by acasing on its leading side to guide the floats up to the overflow weir which discharges into the trough. The said casing may also be shaped to form, with the rising belt, a converging zone. A similar casing, or a continuation of said casing may also be formed on the trailing side of said trough, whereby the materials and liquid which pass under said trough emerge into an expanding zone. The upper part of the casing on the trailing side of the trough leads, into a weir on the trailing side of the trough which discharges into the trough in the reverse direction to the floats weir. Thus a Venturi effect is produced below the trough which intensifies the flow under the trough and thereby carries the semi-floating middlings from the separating zone and imparts an upward impetus to the middlings, means being provided for intercepting this upward flow of middlings and feeding the latter back into the middlings weir in the opposite direction to that of the liquid stream.

The invention will now be described by way of example with reference to the accompanying drawings which show apparatus for cleaning coal.

In the said drawings:

Fig; 1 is a plan.

Fig. 2; is a side elevation.

Fig. 3 is an end elevation of the delivery end of the apparatus.

Fig; 4. is a section on the line IVIV of Fig. 2.

Referring more particularly to the drawings, l is a separating tank having an inclined bottom 2 which is concave in section, and over which is adapted to travel a.- rubber belt 3 the conveying surface ofwhich is transversely troughed as a result of its travelling along the concave bottom 2. The troughing-of' the belt is maintained after it leaves the tank; by means of one or more sets of adjustable mitred idler rollers 4, thereby en abling; the liquid at the shallow end to be contained within the troughing of the belt and independently of the tank. With this arrangement the central portion of the belt is below liquidlevel while the upturned sides of the belt are above liquidlevel. The liquid is thus contained in the troughed belt until it reaches the delivery pulley 5, arid isthereby prevented from overflowing the sides of the belt and discharges over the pulley- 5- with the sinks. The return portion of the belt passes under the tank, over a pair of tandemdriving'pulleys 6, I back to a tail pulley 8 over which it passes to the tank over a set of mitred= idler rollers 9 which trough it to the same contour as that of the bottom 2 prior to its entering: the-tank on the level of the bottom throughend seals ill of the kind described in U. S. Patent No. 2,489,161.

The delivery pulley 5 is mounted on pulley blocks H which themselves are mounted for up and. down adjustment on the side faces of pillars l2, so. that the belt may be raised and lowered at the delivery end relatively to the level of the liquid: medium, and thereby decrease or increasethe amount. of flow-along the belt, and thereby; the speed. of: flow with the belt. The mitrerollers-4' require to .beadjusted to maintain the troughing-of;the belt in accordance with the position it is caused; to take up by the pulley 5.

The above arrangement of the belt drive in dependently' of the delivery pulley 5 enables the latter to be adjustedsubstantially without affecting the driving surface or the longitudinal tension of the belt.

The floats and middlings aredischarged overweirs l5a into the trough l-3 which is of substantially rectangular cross section having a central longitudinal (relativelyto the trough) removable partition plate llwhich divides the trough into. two compartments which. are respectively connected to two separate discharge outlets. Embracing the said trough is a casing [4 having upwardly inclined and declined faces, 15b and lie respectively, on the leading side of the trough, and similar upwardly inclined and declined faces, l5d and 15c respectively, on the trailing side of the trough.

The eifect of this casing, is to lead the floats up the face lEb to the weir l5a, where a paddle l6, serves to press the floats with their carrying liquid up the inclined face of the casing 15 into the trough l3.

The declined face I50 directs the liquid carrying the middlings through the Venturi-like passage formed between the faces 15c and 15c and the conveyor belt. This has the effect of increasing the velocity of flow of the liquid stream so that the middlings, after the floats have been discharged; are effectively carried from the separating zone under the casing [5 into what may be termed the middlings collecting zone where the middlings may finally settle on the belt or rise to the surface according to density. Asthe liquid and middlings emerge from under the face [5c the stream dividesinto a rising portion which.

thereon a. belt pulley l9. by which it. is driven. from a motor 20 through a reductiongear '21.. the other paddlesof' the setcontrolling thetravel.

of the upper layers ofJliquid carrying thefloats.

If the middlings, are to bekept separate from.

the. floats the partition plate 1.4 is. placed. in po.-

sition as shown. so that the two are prevented.

from mixing. If they are to bemixed the partition plateis-removed.

Adjustable lips [5 are, arrangedat. the. weir. edges to vary thedepthpf liquidmediumover. the weirs. By adjustment of these lipstherelative heights of. thefloats and middlings weirs may be varied to allow more or less liquid medium; to flow over. either. of them.. so thatthe. amount.

of flow under the trough. 13. may. becontrolled. The adjustment of the. lips l5! incombination with adjustment of the pulleysB: thus.provides,

control of the, distributionof the flow inthe different zones to suit the travel of. thefioatsmid dlings and sinks.

When the liquid medium comprises a suspension of finely divided solids in water this-adjustment of the lips. I5)v and the, pulley. 51prov=ide an.

improved. control. ofv the. distribution. of flow to. counteract settlement. of. the. suspension" solids.

to maintain uniform. density of. the liquid me.-

path. Settlement is thuscounteracted, and-the density maintained.

The sinks may be assisted upthe portion of. the belt 3. above liquid level-by means-inf. a:ro-

tary paddle 22 whichisdriven throughbevelmeduction gear 23 andaverticalshaft ild rfromthe, belt driving. gear. This paddle. may be fitted with.

5. flexible blades to prevent jamming between the blades and the sinks material. v

Liquid medium is introduced bymeans of a header 25 arranged at the deep or feed end of the tank, and having inlet openings 25a formed therein at different levels.

26 indicates the liquid level.

Additional liquid medium may be introduced at an intermediate point or points as shown, for example, at 2! in the tank sides whereby the flow along the belt may be increased.

In operation the material to be separated is introduced at the feed end of the tank at A where it separates into sinks, middlings and floats as in the above specifications. The liquid medium flows from the inlets 25a in the direc tion of the travel of the belt 3, the lower-most inlet ensuring a flow close above the belt. The upper and intermediate strata of liquid which carry the floats and middlings respectively also move in the same direction towards the trough I3.

When the stream reaches the leading portion of the trough casing 15 the floats are at the surface while the middlings are mostly in the lower portion where they are caused to move at an increased speed under the casing l as above described. The floats are assisted along the surface by the paddles and are fed with some liquid medium by the paddle l6 into the floats portion of the trough I3, while the uprising middlings with some liquid medium are swept backwards by the paddl I! into the middlings portion of the trough [3. When it is not required to keep the middlings separate from the floats, the partition I4 is removed and the products mixed in the trough [3.

The sinks are conveyed upwards by the belt 3 out of the liquid medium over the rollers 4 to discharge, so that the uniflow action of the process is maintained throughout the travel of the liquid medium. By adjusting the height of the discharge pulley 5 the depth, and therefore the amount of liquid medium discharging with the sinks may be varied, so that the speed of liquid flow above the belt 3 may be controlled to suit the speed of travel of the sinks.

At the extreme delivery point of the pulley, rubber skirts may be fitted to prevent the liquid flowing over the sides of the pulley.

I claim:

1. Apparatus for separating solid granular materials in a liquid separating medium of density intermediate those of the solids being separated, comprising a tank adapted to contain a stream of the liquid medium, a uniformly inclined and transversely troughed floor in said tank, a conveyor belt adapted to traverse the floor of said tank, said belt being adapted to conform to the troughed form of said floor and to receive the settled sinks and convey said sinks by frictional contact with the surface of said belt to the surface of the liquid medium, a transversely troughed extension of said belt beyond said tank, a delivery pulley located at a distance beyond the discharge end of the tank with its upper surface slightly below the liquid level in said tank, troughing roller means between the tank end and said pulley, said pulley and said troughing roller means being adapted to carry the portion of said belt which extends beyond the tank, said troughing roller means being 10- cated with their central portions slightly below the liquid level and adapted to lift the edges of the extended portion of said belt in the vicinity of the liquid level whereby the belt is transversely troughed where it leaves the tank and is thereby adapted to contain the overflowing liquid medium after it leaves the tank and to lead it with-the sinks over said delivery pulley, and at the feed end of thetank liquid inlet means adapted to feed liquid medium above the belt to induce flow in the direction of travel of the sinks throughout the length of the carrying portion of said belt, and means independent of the conveyor belt for removing the floats from the surface of the liquid medium intermediate the ends-of the tank.

2. Apparatus for separating solid granular materials in a liquid separating medium of density intermediate :those of the solids being separated, comprising a tank adapted to contain a stream of the liquid medium, a uniformly inclined and transversely troughed floor in said tank, a conveyor belt adapted to traverse the floor of said tank,-said belt being adapted to conform to the troughed form of said floor and to receive the settled sinks and convey said sinks by frictional contact with the surface of said belt to the surface of the liquid medium, a transversely troughed extension of said belt beyond said tank, a delivery pulley located at a distance beyond the discharge end of the tank with its upper surface slightly below the liquid level in said tank, troughing roller means between the tank end and said pulley, said pulley and said troughing roller means being adapted to carry the portion of said belt which extends beyond the tank, said troughing roller means being located with their central portions slightly below the liquid level and adapted to lift the edges of the extended portion of said belt in the vicinity of the liquid level whereby the belt is transversely troughed where it leaves the tank and is thereby adapted to contain the overflowing liquid medium after it leaves the tank and to lead it with the sinks over said delivery pulley, means for vertically adjusting said delivery pulley relatively to said troughing roller means, whereby the longitudinal contour of said belt extension may be modified to vary the amount of liquid medium flowing with the sinks over said delivery pulley, and at the feed end of the tank liquid inlet means adapted to feed liquid medium above the belt to induce flow in the direction of travel of the sinks throughout the length of the carrying portion of said belt, and means independent of the conveyor belt for removing the floats from the surface of the liquid medium intermediate the ends of the tank.

3. Apparatus for separating solid granular materials in a liquid separating medium of density intermediate those of the solids being separated, comprising a tank adapted to contain a stream of the liquid medium, a uniformly inclined and transversely troughed floor in said tank, a conveyor belt adapted to'traverse the floor of said tank, said belt being adapted to conform to the troughed form of said fioor and to receive the settled sinks and. convey said sinks by frictional contact with the surface of said belt to the surface of the liquid medium, a transversely troughed extension of said belt beyond said tank, a delivery pulley located at a distance beyond the discharge end of the tank with its upper surface slightly below the liquid level in said tank, troughing roller means between the tank end and. said pulley, said pulley and said troughing roller means being adapted to carry the portion of said belt which extends beyond the tank, said troughingroller means being locatedwith their central portions slightly'below the liquid level and adapted to lift the edges of the extended portion of saidbelt in the vicinity of the liquid level whereby the belt is transversely troughed where it leaves the tank andis thereby adapted to contain the overflowing liquid medium after it leaves the tank and to lead it with the sinks over said delivery pulley,-pil1ar means for carrying said pulley, pulley carrying blocks, said pillar means having faces on which said blocks are adjustably mounted, tandem driving pulleys for driving said belt independently of said delivery pulley, said driving pulleysbeing located so that the portion of the belt between the belt receiving pulley of said tandem driving pulleysv and the delivery pulley is substantially mrmarw said pillar faces to enable said delivery pulley m be raised or lowered without affecting the driving surface and the longitudinal tension of said belt, andat thefeed end of the tank' liquidinlet means adapted to feed liquid medium' above 8 the belt to induce flow in the direction of travel of the sinks throughout the length of the carrying portion of said belt, and means independent of the conveyor belt for removing the floats from the surface of the liquid medium intermediate the ends of the tank.

FRANK FROST RIDLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. APPARATUS FOR SEPARATING SOLID GRANULAR MATERIALS IN A LIQUID SEPARATING MEDIUM OF DENSITY INTERMEDIATE THOSE OF THE SOLIDS BEING SEPARATED, COMPRISING A TANK ADAPTED TO CONTAIN A STREAM OF THE LIQUID MEDIUM, A UNIFORMLY INCLINED AND TRASVERSELY TROUGHED FLOOR IN SAID TANK, A CONVEYOR BELT ADAPTED TO TRAVERSE THE FLOOR OF SAID TANK, SAID BELT BEING ADAPTED TO CONFORM TO THE TROUGHED FORM OF SAID FLOOR AND TO RECEIVE THE SETTLED SINKS AND CONVEY SAID SINKS BY FRICTIONAL CONTACT WITH THE SURFACE OF SAID BELT TO THE SURFACE OF THE LIQUID MEDIUM, A TRANSVERSELY TROUGHED EXTENSION OF SAID BELT BEYOUD SAID TANK, A DELIVERY PULLEY LOCATED AT A DISTANCE BEYOUND THE DISCHARGE END OF THE TANK WITH ITS UPPER SURFACE SLIGHTLY BELOW THE LIQUID LEVEL IN SAID TANK, TROUGHING ROLLER MEANS BETWEEN THE TANK END AND SAID PULLEY, SAID PULLEY AND SAID TROUGHING ROLLER MEANS BEING ADAPTED TO CARRY THE PORTION OF SAID BELT WHICH EXTENDS BEYOND 